In the production of certain paper products such as facial tissues, paper towels, napkins, and the like, an aqueous slurry of wood fibers (pulp) is deposited on a moving foraminous fabric in such a manner so as to form a thin layer or web of fibers. The resulting web is then dewatered, dried, creped, and wound up on large rolls.
Creping of the web is a well known method for improving the properties of softness and bulk by breaking interfiber bonds. This is commonly accomplished by adhering the web to the surface of a large, rotating drum (Yankee dryer) and thereafter dislodging the web with a doctor blade. As the web contacts the edge of the doctor blade, it experiences compressive forces which disrupt the internal structure and cause the web to buckle, forming a series of peaks and valleys in the web as it leaves the doctor blade. The creping process with the attendant use of creping adhesives is well known in the industry and is adequately described in U.S. Pat. No. 4,304,635 issued Dec. 8, 1981 to H. E. Grube and T. D. Ries, which is hereby incorporated by reference.
More recently, drying of the web by a method known as throughdrying has received considerable attention because of its contribution to improved bulk and softness of the web during drying. This is generally accomplished by passing hot air through the web to effect partial drying prior to pressing the web against the Yankee dryer to finish the drying process. However, one disadvantage of partial drying prior to the Yankee is that the resulting partially dried web requires the addition of a creping adhesive to the surface of the Yankee (or any other creping cylinder which may be used) in order to provide sufficient adhesion of the web to the cylinder necessary to obtain proper creping. This was generally not necessary in more conventional processes where the high moisture content of the web provided sufficient adhesion to the Yankee cylinder. Although creping adhesives may have been used previously from time to time to supplement the natural adhesion of the wet web, the need for creping adhesives has been greatly increased with the advent of throughdrying.
A creping adhesive commonly used for throughdrying processes consists of a blend of ethylene/vinyl acetate copolymer and polyvinyl alcohol. This composition is satisfactory for a wide range of applications, but suffers from buildup of water insoluble residues on process fabrics. The disclosed adhesive comprising ethylene oxide/propylene oxide copolymer and polyvinyl alcohol provides good web bonding properties to the surface of the Yankee dryer while allowing easy cleanup of residues on process fabrics by virtue of the adhesive's water solubility.